Synthesizing existing work from diverse disciplines, this paper introduces a culture-gene coevolutionary approach to human behavior and psychology, and applies it to the evolution of cooperation. After a general discussion of cooperation in humans, this paper summarizes Dual Inheritance Theory and shows how cultural transmission can be brought under the Darwinian umbrella in order to analyze how culture and genes coevolve and jointly influence human behavior and psychology. We then present a generally applicable mathematical characterization of the problem of cooperation. From a Dual Inheritance perspective, we review and discuss work on kinship, reciprocity, reputation, social norms, and ethnicity, and their application to solving the problem of cooperation. (c) 2006 Published by Elsevier B.V.

Researchers from across the social sciences have found consistent deviations from the predictions of the canonical model of self-interest in hundreds of experiments front around the world. This research, however, cannot determine whether the uniformity results from universal patterns of human behavior or from the limited cultural variation available among the University students used in virtually all prior experimental work. To address this, we undertook a cross-cultural study of behavior in ultimatum, public goods, and dictator games in a range of small-scale societies exhibiting a wide variety of economic and cultural conditions. We found, first, that the canonical model - based on self-interest - fails in all of the societies studied. Second, our data reveal substantially more behavioral variability across social groups than has been found in previous research. Third, group-level differences in economic organization and the structure of social interactions explain a substantial portion of the behavioral variation across societies: the higher the degree of market integration and the higher the payoffs to cooperation in everyday life, the greater the level of prosociality expressed in experimental games. Fourth, the available individual-level economic and demographic variables do not consistently explain game behavior, either within or across groups. Fifth, in many cases experimental play appears to reflect the common interactional patterns of everyday life.

We would like to thank the commentators for their generous comments, valuable insights and helpful suggestions. We begin this response by discussing the selfishness axiom and the importance of the preferences, beliefs, and constraints framework as away of modeling some of the proximate influences on human behavior. Next, we broaden the discussion to ultimate-level (that is evolutionary) explanations, where we review and clarify gene-culture coevolutionary theory, and then tackle the possibility that evolutionary approaches that exclude culture might be sufficient to explain the data. Finally, we consider various methodological and epistemological concerns expressed by our commentators.

Over the last decade, research in experimental economics has emphatically falsified the textbook representation of Homo economicus. Literally hundreds of experiments suggest that people care not only about their own material payoffs, but they also care about such things as fairness and reciprocity. However, this research left a fundamental question remain unanswered: Are these non-selfish motives a stable aspect of human nature; or, are they substantially modulated economic, social and cultural environments? Prior to this book, the available experimental research could not begin to address this question because virtually all subjects had been university students, and while there are cultural differences among student populations throughout the world, these differences are small compared to the full range of human social and cultural environments. While a vast amount of ethnographic and historical research suggests that people's motives are influenced by the economic, social, and cultural environments, such methods,can only yield circumstantial evidence about human motives. As the longstanding disagreements within the cultural and historical disciplines attest, many different models of human action are consistent with the ethnographic and historical record.

In both testing the universally of previous findings, and in bridging the mythical chasm between ethnographic and experimental approaches, this volume deploys some of the principle experiments (which have been used to show non-selfish motives in university students) in combination with ethnographic data to explore the motives that underlie the diversity of human sociality. Twelve experienced field researchers performed the same experiments in fifteen small-scale societies exhibiting a wide variety of economic and cultural conditions. Our results can be summarized in five points: first, there is no society in which experimental behavior is consistent with the canonical model of rational self-interest; second there is much more variation between groups than has been previously reported; third, differences between societies in market integration and the importance of cooperation explain a substantial portion of the behavioral variation between groups; fourth, individual-level economic and demographic variables do not explain behavior within or across groups; fifth, experimental play often mirrors patterns of interaction found everyday life.